The present invention relates to a pressure sensor integrated glow plug in which a pressure sensor for detecting the pressure inside a cylinder is integrated into a sheathed glow plug used to aid the starting of a diesel engine.
Conventionally, in diesel engines, which are self-igniting internal combustion engines, glow plugs are disposed inside the cylinders. Furthermore, in recent years, pressure sensor integrated glow plugs, in which a pressure sensor for detecting the pressure inside the cylinder is integrated with the glow plug, have been put into practical use.
For example, a pressure sensor integrated glow plug is configured to include a housing for insertion inside a cylinder, a heater element held in the housing with its distal end projecting from the housing, and a pressure sensor disposed between the heater element and the housing. In this pressure sensor integrated glow plug, the heater element is held in the housing by a flexible member such as a bellows or a diaphragm, the heater element is displaced in an axial direction inside the housing by the pressure inside the cylinder, and the pressure sensor can detect the pressure inside the cylinder because of this displacement.
In such a glow plug, in order to make it possible to stably detect the pressure over a long period of time, the flexibility of the flexible member must be maintained. That is, the heater element must be kept from being mechanically restrained in the section outside the flexible member. However, the glow plug is exposed inside the cylinder and used, and when uncombusted fuel components or the like generated inside the cylinder build up between the heater element and the housing, there is the concern that the heater element will become restrained in the housing and will no longer be able to transmit the pressure inside the cylinder to the pressure sensor.
For that reason, proposals have been made to prevent the build-up of uncombusted fuel components by filling the space between the heater element and the housing with a fluid seal material or coating the surface of the heater element with an oxidation catalyst (e.g., see JP-A-2009-520941 and JP-A-2009-203939).